Field of the Invention
The invention relates to a turbine shaft which extends along a principal axis and has an outer surface. The invention also relates to a method for cooling a turbine shaft.
The use of steam at relatively high pressures and temperatures, especially at so-called supercritical steam conditions, with a temperature of, for example, above 550.degree. C. contributes to an increase in efficiency of a steam turbine. The use of steam with such a steam condition places increased demands on a steam-turbine shaft which is subjected to the steam.
German Published, Non-Prosecuted Patent Application DE 32 09 506 A1, to which European Patent 0 088 944 B1 corresponds, describes a shaft shield configuration with swirl cooling for a region of a turbine shaft which is directly subjected to live steam after it flows into the turbine. In swirl cooling, steam flows through four tangential holes in the shaft shield configuration into a region between the shaft shield configuration and the turbine shaft in the direction of rotation of the latter. In the process, the steam expands and the temperature falls, thereby cooling the turbine shaft. The shaft shield configuration is connected in a steam-tight manner to a row of fixed blades. Through the use of the swirl cooling, it is possible to achieve a temperature reduction of the turbine shaft in the vicinity of the rotor shield configuration of about 15 K. Nozzles are introduced into the shaft shield configuration for swirl cooling and, as seen in the direction of rotation of the turbine shaft, they open tangentially into an annular passage formed between the turbine shaft and the shaft shield configuration.
Swiss Patent No. 259 566 describes a rotor for a rotary machine, a rotor for gas turbines, which is transversely divided relative to a rotation axis, is composed of several parts and is held together by at least one central tie rod that penetrates at least a partial number of the rotor parts. The rotor is cooled, at least at its hottest points, through an air stream or gas stream.
German Published, Non-Prosecuted Patent Application DE-OS 15 51 210 describes a rotor for a high-powered steam turbine in a disc-type construction. The discs are connected to each other by a central tie rod. They have an asymmetrically shaped saw-toothing at rims which are tightened together.